Heretofore, various methods for controlling soil-borne plant diseases are known, including soil disinfection, the use of resistant cultivars or resistant rootstocks, etc. Among them, soil fumigants exhibit a higher effect, but lead to problems with environmental conservation and worker's safety. Recently, specially cultivated agricultural products or organic agricultural products have received attention in view of food safety, and thus controlling methods alternative to the use of chemical pesticides have been studied. In these situations, agents for controlling diseases and pestilences (i.e., agents capable of controlling damages caused by phytopathogenic microorganisms or pests), which utilize microorganisms, have been researched and developed, including microorganism pesticides containing filamentous fungi or bacteria as an active ingredient.
Genus Plectosphaerella is a filamentous fungus widely distributed around the world, which has been studied as microorganism pesticides for controlling nematodes such as cyst nematode or weeds such as catchweed (see, for example, Non-Patent Literature 1 and Patent Literature 1). However, it has not reported that microorganisms belonging to genus Plectosphaerella have a controlling effect on plant diseases.